浙西北地区二叠系和三叠系的构造变形样式及其大地构造意义初步研究

浙西下三叠系统政棠组(T_1zh)发育有典型的鲍马序列,是一套深水相浊积岩建造;区域构造环境初步分析表明浙西北地区具被动大陆边缘沉积楔特征。下三叠系统政棠组(T_1zh)与二叠系协调变形,其构造变形样式总体上以向西北逆冲的冲褶席(duplex)~ 为特征,变形强度自南东向北西呈递减趋势。上三叠统乌灶组(T_3w)为含煤陆相磨拉石盆地建造,变形样式以宽缓褶皱和逆断层组合为主。该区大地构造相主要为前陆褶皱冲断带相,而土三叠统乌灶组(T_3w)为前陆磨拉石盆地相,二者对浙西北地区早中生代造山作用的研究具重要意义。

Structures of the Permian and Triassic and Their Tectonic Significance, NW Zhejiang, SE China

(1) There are typical Bouma Sequences in the Zhengtang Fm. (T1 zh ), indicating the characteristics of turbidite; Sedimentary analysis suggests a passive continental margin with southeast-silting slope: Sedimentary structures viewed a complicated assembly imbricated by large amounts of inverted and normal stratigraphic sequences with similar occurrences, which shows many inverted tight folds; Some big-scale inverted tight folds with northwest-ward hinge can be fully investigated with formerlimb thrust and backlimb thrust. From SE to NW there are foreland diping duplexs, antiformal stacks and hinterland dipping duplexs with fold-style varing gradully from big-scale tight fold to mid-scale chevron fold, then to cyclindrical fold. (2) The Upper Triassic (T3 w ) shows sediments of the molasse basin with high-angle thrusting and folding; (3) The tectonic analysis of NW Zhejiang indicates the main tectonic facies is the foreland fold-thrust belt with northwest-direction thrusting. Together with the molasse basin of the Late Triassic, the Early Mesozoic collision orogen can be recognized in SE China.